Facebook forms partnerships with firms including Symantec, McAfee and Microsoft in an effort to keep its users from sharing links to sites that install malware.

SAN FRANCISCO — As it closes in on 1 billion users, Facebook Inc. has formed partnerships with five security software outfits to crack down on pfishing schemes.

Facebook said Wednesday that Microsoft Corp., McAfee Inc., Trend Micro Inc., Sophos Ltd. and Symantec Corp. will join the fight to keep its users from sharing links to sites that install malware. Facebook also has its own tools in its arsenal and a vast database of malicious URLs.

Facebook users, who number more than 900 million, post a ton of links, some from blacklisted sites. Now Facebook will warn you when you click on a site it suspects could pose a threat to your computer.

As part of the new partnerships, users can sign up for free six-month subscriptions to anti-virus software to install on their computers.

Facebook is looking to shore up security issues that have plagued its website. Security vendors are hoping to hook some paying customers.